/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.iotdb.tsfile.encoding.decoder;

import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
import org.apache.iotdb.tsfile.utils.ReadWriteForEncodingUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.nio.ByteBuffer;

public class LongZigzagDecoder extends Decoder {
    private static final Logger logger = LoggerFactory.getLogger(IntZigzagDecoder.class);

    /**
     * how many bytes for all encoded data in input stream.
     */
    private int length;

    /**
     * number of encoded data.
     */
    private int number;

    /**
     * number of data left for reading in current buffer.
     */
    private int currentCount;

    /**
     * each time decoder receives a inputstream, decoder creates a buffer to save all encoded data.
     */
    private ByteBuffer byteCache;

    public LongZigzagDecoder() {
        super(TSEncoding.ZIGZAG);
        this.reset();
        logger.debug("tsfile-encoding LongZigzagDecoder: long zigzag decoder");
    }

    /**
     * decoding
     */
    @Override
    public long readLong(ByteBuffer buffer) {
        if (currentCount == 0) {
            reset();
            getLengthAndNumber(buffer);
            currentCount = number;
        }
        long n = 0;
        int i = 0;
        long b = 0;

        while (byteCache.hasRemaining() && ((b = byteCache.get()) & 0x80) != 0) {
            n |= (b & 0x7F) << i;
            i += 7;
        }
        n = n | (b << i);
        currentCount--;
        return (n >>> 1) ^ -(n & 1); // back to two's-complement
    }

    private void getLengthAndNumber(ByteBuffer buffer) {
        this.length = ReadWriteForEncodingUtils.readUnsignedVarInt(buffer);
        this.number = ReadWriteForEncodingUtils.readUnsignedVarInt(buffer);
        byte[] tmp = new byte[length];
        buffer.get(tmp, 0, length);
        this.byteCache = ByteBuffer.wrap(tmp);
    }

    @Override
    public boolean hasNext(ByteBuffer buffer) {
        if (currentCount > 0 || buffer.remaining() > 0) {
            return true;
        }
        return false;
    }

    @Override
    public void reset() {
        this.length = 0;
        this.number = 0;
        this.currentCount = 0;
        if (this.byteCache == null) {
            this.byteCache = ByteBuffer.allocate(0);
        } else {
            this.byteCache.position(0);
        }
    }
}
